KTM 250 Fouls plugs too much!

[VCHSS4]

My 1990 KTM 250 EXC fouled three plugs while riding. I put new Boyesen Pro Series reeds in the night before. Needle clip postion is 1st from top. Still fouls plugs. What should I do to stop this? Drop the main jet from a 185 to a 182 or 180?

 

[D Lafleur]

VC,
We need to know what carb, needle, slide, and pilot jet you have in the bike.
If you have a PWK Keihen carb I would say you have too much main jet, but it could be other things working against you. A 185 main jet is big, if you live anywhere above sea level that is not in dry cold country, I would say you have too much main jet. A 180 may be a good start. Does the bike run decent at less than 1/2 throttle? If so then I would look at the main as the first change. The condition of the motor is also a factor. Old motors can have other troubles that will affect the jetting.

 

[katoom114]

I had a 96 250 EXC with the same problem. I had to replace the crank seals. If it smokes or the plug seems oily, this may be your problem.

 

[JCW]

sure sounds like jetting is too rich`

Ride the bike the way you ride it and shut it off quickly and look at the plug. If there's black gooooy stuff on it, you are probably too rich. Check out "Canadian Dave's KDX forum on DRN" He has an excellent explanation of 2 stroke jetting.

I bet you're too rich and a smaller main jet is in order. I wouldn't move over 4 points per change (184-180, etc.).
You don't want to move too far to quick and lean it out.

JCW

 

[SFO]

I had a 90 250 exc and there was a ktm update for jetting the
Keihin carb.
It had a leaner slide as well as a different needle and pilot.
When I was done the bike made 43rwhp on a dynojet.
There is also an updated powervalve flapper as the oem ones would break in half and waste the top end.
I also had good luck with juggling powervalve springs in this motor.
I ended up with the spring from a 94 mx 250 model.